Which of the Following Represents the Point at Which an Investigation

Which of the following represents the point at which an investigation becomes an interrogation?

A) when a person requests the presence of an attorney, regardless of his or her status as a suspect in a crime
B) when the captain says, "Go"
C) when the police have evidence beyond a reasonable doubt who perpetrated a crime
D) when the investigation is no longer a general inquiry but has begun to focus on a particular suspect